feat(typescript): add coverage-summary to the TypeScript bundle

Last language in the coverage-summary fan-out, after Elisp, Python, and Go. Same kernel: count every source file on disk that's absent from the coverage report as 0% and weight the project number by file, so an untested file stays visible instead of being averaged away.

The script at languages/typescript/claude/scripts/coverage-summary.js parses an Istanbul json-summary report (the coverage-summary.json that c8, Vitest, and Jest all emit), takes per-file statements covered over total, and reports a file-weighted number plus the missing files. It walks the source dir for .ts/.js, skipping test files, declarations, and node_modules. Node built-ins only, so it runs via node with no install, and it doesn't reimplement the per-file table nyc already prints.

Tests are black-box, run with node's own test runner: a temp tree plus a json-summary report, the script invoked via node, output asserted. They cover missing-file detection, all-tracked, test-file and node_modules exclusion, and the missing-report error. make test gained a node --test discovery path for languages/*/tests, guarded so environments without Node skip it cleanly. As with Python, the TypeScript bundle had no gitignore-add.txt, which would have left the script un-gitignored on install, so I added one.

This finishes the fan-out: coverage-summary now ships in all four bundles, each parsing its own tool's report behind the same file-weighted, missing-as-0% kernel. I proved the Go and TypeScript scripts by running them (Go against a live profile, TS against a synthetic report and the CLI). Python and TypeScript weren't run against a live coverage tool, since neither coverage.py nor nyc is installed here, so the first adopter of each should check against a real report.

1 files changed, 45 insertions, 0 deletions

diff --git a/languages/typescript/coverage-makefile.txt b/languages/typescript/coverage-makefile.txt
new file mode 100644
index 0000000..64c7fcd
--- /dev/null
+++ b/languages/typescript/coverage-makefile.txt
@@ -0,0 +1,45 @@
+# TypeScript / JavaScript coverage — Makefile fragment + setup recommendation
+#
+# This file is owned by the project, not the rulesets bundle. The bundle never
+# edits your Makefile. Copy the two targets below into your own Makefile (and
+# adjust the variables at the top), then delete this file or keep it as a note.
+#
+# What you get:
+#   make coverage          runs the suite under c8 and writes an Istanbul
+#                          json-summary report plus c8's own text table
+#   make coverage-summary  prints a file-weighted project number and every
+#                          source file on disk absent from the report, at 0%.
+#
+# Why the summary matters: a module no test imports never appears in the
+# Istanbul report, so a statement-weighted total silently skips it. The summary
+# weights by file and counts a missing file as 0%, so untested files stay
+# visible. It does not reimplement the per-file table — nyc/c8 already print it.
+#
+# ---------------------------------------------------------------------------
+# Prerequisite: an Istanbul json-summary report.
+#
+#   c8:      npx c8 --reporter=json-summary --reporter=text npm test
+#   vitest:  vitest run --coverage --coverage.reporter=json-summary
+#   jest:    jest --coverage --coverageReporters=json-summary
+#
+# All three write coverage/coverage-summary.json. The summary script needs
+# nothing beyond Node's standard library — it parses the JSON.
+# ---------------------------------------------------------------------------
+
+# Variables — adjust to your layout.
+NODE             ?= node
+SOURCE_DIR       ?= src
+COVERAGE_FILE    ?= coverage/coverage-summary.json
+# The summary script ships with the bundle under .claude/scripts/ (gitignored).
+COVERAGE_SUMMARY ?= .claude/scripts/coverage-summary.js
+
+coverage:
+	@npx c8 --reporter=json-summary --reporter=text npm test
+	@$(MAKE) coverage-summary
+
+coverage-summary:
+	@if [ ! -f $(COVERAGE_FILE) ]; then \
+		echo "[!] No coverage file at $(COVERAGE_FILE). Run 'make coverage' first."; \
+		exit 1; \
+	fi
+	@$(NODE) $(COVERAGE_SUMMARY) $(COVERAGE_FILE) $(SOURCE_DIR) .